What is CVE-2026-9903?

CVE-2026-9903 is a medium-severity vulnerability in Google Chrome, classified under Improper Input Validation. CVSS score: 5.0/10. Published 2026-05-28.

How severe is CVE-2026-9903?

Medium severity. CVSS v3 base score is 5.0 out of 10.

Improper input validation in Google Chrome

CVE-2026-9903

Insufficient validation of untrusted input in Site Isolation in Google Chrome prior to 148.0.7778.216 allowed a remote attacker who had compromised the renderer process to bypass site isolation via a crafted MHTML page. (Chromium security severity: High)

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2026-05-28 · last modified 2026-07-21.

CVSS v3 metric

CVSS v3 base score 5.0 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.002 (8.9th percentile), scored 2026-10-07.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 8.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Google Chrome — versions 148.0.7778.216

Weakness classification (CWE)

CWE-20 — Improper Input Validation

References

chromereleases.googleblog.com/2026/05/stable-channel-update-for-desktop_0877304… (Release Notes)
issues.chromium.org/issues/498783665 (Permissions Required)

Frequently asked questions

What is CVE-2026-9903?: CVE-2026-9903 is a medium-severity vulnerability in Google Chrome, classified under Improper Input Validation. CVSS score: 5.0/10. Published 2026-05-28.
How severe is CVE-2026-9903?: Medium severity. CVSS v3 base score is 5.0 out of 10.